1. Field of the Invention
The present invention relates to a halftone-image processing device for generating output image data by determining pixels for forming output dots based on input image data, the input image data having density data for a plurality of pixels.
2. Description of Related Art
A halftone processing method is a method for expressing gradations of inputted image data through dot distribution. Here, the inputted image data includes density data for a plurality of pixels. The error diffusion process and the dither process are representative examples of the halftone processing method.
Errors are generated at pixels when the inputted image data at the pixels is binarized to determine whether or not to output dots based on the density values of the pixels. According to the error diffusion method, the errors are distributed to other pixels that are located adjacent to the subject pixel and that are not yet processed. It is possible to reduce the difference in density between the inputted image data and the outputted image data for the overall image. Error diffusion is currently the most frequently used process and is used for reproducing high-quality images.
The error diffusion method, however, requires much more processing time than the dither method. Accordingly, various efforts have been made to speed up the error diffusion process. Japanese Patent No. 2745527 and U.S. Pat. No. 5,031,050 have proposed combining the dither method and the error diffusion method.